1. Field of the Invention
The present invention relates generally to medical methods and systems. More particularly, the invention is directed to methods and systems for treating and determining physiologic characteristics of body lumens such as the esophagus.
The human body has a number of internal body lumens or cavities located within, many of which have an inner lining or layer. These inner linings can be susceptible to disease. In some cases, surgical intervention can be required to remove the inner lining in order to prevent the spread of disease to otherwise healthy tissue located nearby.
Those with persistent problems or inappropriate relaxation of the lower esophageal sphincter can develop a condition known as gastro esophageal reflux disease, manifested by classic symptoms of heartburn and regurgitation of gastric and intestinal contents. The causative agent for such problems may vary. Patients with severe forms of gastroesophageal reflux disease, no matter what the cause, can sometimes develop secondary damage of the esophagus due to the interaction of gastric or intestinal contents with esophageal cells not designed to experience such interaction.
The esophagus is composed of three primary tissue layers; a superficial mucosal layer lined by squamous epithelial cells, a middle submucosal layer and a deeper muscle layer. When gastroesophageal reflux occurs, the superficial squamous epithelial cells are exposed to gastric acid, along with intestinal bile acids and enzymes. This exposure may be tolerated, but in some cases can lead to damage and alteration of the squamous cells, causing them to change into taller, specialized columnar epithelial cells. This metaplastic change of the mucosal epithelium from squamous cells to columnar cells is called Barrett's esophagus, named after the British surgeon who originally described the condition.
Barrett's esophagus has important clinical consequences, since the Barrett's columnar cells can, in some patients, become dysplastic and then progress to a certain type of deadly cancer of the esophagus. The presence of Barrett's esophagus is the main risk factor for the development of adenocarcinoma of the esophagus.
Accordingly, attention has been focused on identifying and removing this abnormal Barrett's columnar epithelium in order to mitigate more severe implications for the patient. Devices and methods for treating abnormal body tissue by application of various forms of energy to such tissue have been described, such as radio frequency ablation. However, without precise control of the depth of penetration of the energy means, these methods and devices are deficient. Uncontrolled energy application can penetrate too deeply into the esophageal wall, beyond the mucosa and submucosal layers, into the muscularis externa, potentially causing esophageal perforation, stricture or bleeding. Accordingly, proper administration of the correct amount of treatment energy to the tissue can be facilitated by knowledge of the size of the esophagus and area to be treated.
Additionally, medical procedures for treating Barrett's esophagus typically involve deployment of an expandable catheter inside the esophagus. Expandable catheters are preferred because the profile of the catheter is ideally as small as possible to allow for ease of delivery, while treatment of the esophagus is most efficiently performed when the catheter is at or slightly larger than the diameter of the esophageal wall. Proper sizing and/or pressurization of the delivery device is therefore desirable to prevent over-distension of the organ, which could result in harm to the organ, or under-expansion of the catheter, which often results in incomplete treatment. Accordingly, accurate and simple measurement of the size of the lumen and control of the pressure of the catheter on the lumen surface promotes the proper engagement and delivery of energy to the luminal wall so that a uniform and controlled depth of treatment can be administered. In addition to calculating luminal dimensions, the compliance of the lumen can be determined by measuring the cross section of the lumen at two or more pressure values.
Therefore, it would be advantageous to have methods and systems for accurately determining in vivo the size and optionally the compliance of a body lumen such as the esophagus. In addition, it would be desirable to provide a method and system for treating the body lumen once having determined its size. At least some of these objectives will be met by the present invention.
2. Description of the Background Art
U.S. Pat. No. 5,275,169 describes apparatus and methods for determining physiologic characteristics of blood vessels. The device measures the diameter and wall compliance of the blood vessel, and does not administer treatment. Additionally, the method relies on using only an incompressible fluid to inflate a balloon inside a blood vessel. Other patents of interest include U.S. Pat. Nos. 6,010,511; 6,039,701; and 6,551,310.